We seek support to investigate the anabolic effects of growth hormone (GH) on body composition in children with a genetic form of obesity, Prader-Willi Syndrome (PWS). We have begun to study the metabolic effects of GH on body composition including linear growth rate, bone density, nutrient intake, and cardiovascular risk factors including resting energy expenditure, lean body mass and percent body fat, muscle strength and agility, pulmonary function, as well as carbohydrate and lipid metabolism. This patient population provides a model with known risk factors for genetic obesity, and metabolic consequences of growth hormone deficiency. Recent investigations have shown anabolic effects of GH improving body composition, while decreasing obesity and other cardiovascular risk factors. We have been awarded peer reviewed funding for a comprehensive controlled study, which provides a unique opportunity to engage in multi-disciplinary clinical research. However, since the time of this clinical grant award, we have added an additional facet to the study: the measurement of resting energy expenditure (REE). Sufficient funds have been obtained to accomplish the majority of study objectives, but not for REE measurements. The measurement of REE utilizing respiratory quotient measurements contributes substantial scientific value to the study protocol, and will be directly applicable to future investigations of metabolic effects of GH and other anabolic hormones on body composition. This assessment will provide important information about factors leading to abnormal body composition in PWS, while further preparing the fellow to conduct important future investigations of the metabolic effects of GH on body composition and obesity.